The present invention relates to an inflatable occupant restraint system commonly referred to as air bags. More particularly, the present invention relates to an apparatus and method of utilization of an aspirated/vented air bag system particularly useful in automotive vehicles.
It is well known in vehicle occupant restraint systems to provide an inflatable nylon-like fabric air bag which is inflated by a gas generator. The gas generator for the passenger inflatable restraint system is preferably a cylindrical metal housing which contains chemicals such as sodium azide and has ports therein through which gases generated by a chemical reaction within the cylinder may be exhausted into the inflatable cushion to inflate the cushion.
To reach the desired expansion of the cushion requires a relatively large amount of gas, which in turn requires a fairly large generator.
It is also necessary to be able to quickly deflate the cushion to control normal system performance and for instances wherein the cushion may engage an obstruction, such as an occupant in an unusual seating position. In prior air bag systems, various devices have been employed to vent the cushion, such as with external cushion bag vents. In operation, when the cushion is filled and unfolded to a given position, the vents become active and inflation gas may be exhausted. Such exhaust means are useful, but they create the potential that the cushion may shift and block all or part of a vent. The above-noted occurrence prevents gas from being exhausted from the cushion at a maximum rate. Another potential problem encountered with external cushion bag vents is that they exhaust inflation gases directly into the occupant compartment. Finally, because of their location on the cushion, external vents do not have the ability to alleviate "break out" forces. Break out is the initial part of a deployment where a folded cushion is forced through a protective cover.
An additional requirement which has been imposed by the trend toward stiff crash pulse vehicles is an increase in the speed of inflation. The more aggressive inflation rate greatly increases the break out forces generated.
An attempt to meet the above concerns has been brought forth by the development of vented housing vehicle air bag systems, by which it is meant that inflation gases may be vented through the housing instead of external cushion vents.
Venting through the housing has seen limited use. However, air bag systems which use vented housings have cushion attachment techniques which mount the cushion around the mouth of the housing, which then requires twelve or more rivets to attach the cushion bag with a flange along an open end of the housing. The large number of rivets for attaching the cushion is a cost disadvantage when assembly, part and tooling costs are considered. Also, with prior vented housings, after a deployment, the inflator (located within the housing near the vents) is exposed to the air under the instrument panel, which is oxygen-rich.